The present invention provides high performance foams comprised of liquid crystal polymers. The foams of the present invention exhibit enhanced mechanical properties.
Foamed plastics are very useful in those applications where enhanced mechanical properties such as a high strength to weight ratio is desirable.
There are many applications for lightweight high performance foamed articles in transportation vehicles, building materials, industrial equipment and business machines, among others. However, no industry demands more lightweight, high performance products than the transportation industry. Particularly in the automobile industry, the principal applications involve structural elements as well as applications under the hood. The structural elements such as trunks, hoods and doors require high mechanical properties. The under the hood applications require excellent resistance to solvents as well as the ability to resist high temperatures.
However, when conventional isotropic polymers are foamed for use in such applications, the advantageous reduction in weight is unfortunately accompanied by a significant reduction in desirable mechanical properties such as tensile strength, impact strength and initial modulus. Thus, the range of applications of foamed conventional plastics is rather limited.
It is known in the art that unfoamed articles of liquid crystal polymers fabricated by conventional methods such as extrusion or injection molding have very high anisotropy of physical properties between the machine direction (MD) and the transverse direction (TD). This leads to very poor TD properties although the MD properties are very suitable. In addition, such articles have very distinct skin-core morphology along the cross section with the core being essentially unoriented.
It is also known that the highly aromatic liquid crystal polymers possess excellent high temperature stability and flame resistance as well as excellent solvent resistance and that foams of liquid crystal polymers may be provided. See U.S. Pat. Nos. 3,778,410; 3,804,805; 3,859,251; 3,890,256; 4,238,600; and published PCT application No. W079/01030.
It is also known to those skilled in the art that the heat treatment of shaped articles of liquid crystal polymers increases its melting point, molecular weight and mechanical properties. See, for example, U.S. Pat. Nos. 3,975,487; 4,183,895; and 4,247,514.